It shouldn’t make a difference whether you ask at the transfer desk or at the check-in desks. If anything, the staff at the TRANSFER (check-in) desks might be even more amenable and better prepared to process such requests swiftly.

As others have said already, SQ seem to be quite open to allowing you to change to an earlier flight if it suits them. I have frequently been able to do so ex MNL, but have never tried it the other way around.

I’d suggest that you don’t worry about it too much in advance, ask politely to be allowed to travel on the earlier flight on the date of travel, and if it doesn’t work out, there are hardly any better airports in the world to hang out at for several hours.